The present invention relates to power conversion circuitry and circuit operating methods, and, more particularly, to circuitry which can operate at very high frequency (VHF) in converting a DC voltage from one level to another level.
Radio frequency (RF) circuitry and digital circuitry have increasingly employed integrated circuits and other microcircuits to reduce apparatus size and weight while providing reliable operation with necessary and desired functioning. As a result, lower DC supply voltages have been needed, but, in many conventional power supply systems such as those in radar circuitry, large DC current distribution is associated with such lower DC voltages. In turn, large currents produce significant voltage drops across power transmitting conductors in the power distribution system, thereby imposing a requirement for greater conductor sizes and weights and complicating the process of achieving DC voltage regulation accuracy.
As disclosed in a commonly assigned patent application entitled PULSED RADAR APPARATUS AND METHOD EMPLOYING POWER DISTRIBUTION SYSTEM HAVING REDUCED COST AND WEIGHT AND ENHANCED EFFICIENCY AND RELIABILITY, Ser. No. 09/041,214, concurrently filed herewith by E. Rich and A. Tarrillo, and hereby incorporated by reference, a distributed power supply delivery system can provide an improved supply of low DC voltage power with use of a VHF DC-DC converter. In a distributed system, distributed power modules deliver power closer to the load point with higher voltage operation at higher levels of the system, thereby reducing the large current otherwise supplied by a central power supply.
In converting DC voltages to lower values in power supply systems, VHF switching, if available, can contribute significantly to reduction in the size and weight of the power supply system and the electronic circuitry associated with the power supply system. Further, communication products, characterized with sensitive data processing, have specifically needed higher (i.e. VHF) DC-DC voltage converter switching frequencies, since power supply operation with a frequency greater than the communication channel frequency minimizes noise/spur interference and eliminates stringent filter requirements.
VHF operation of a DC-DC voltage converter can reduce impedance magnitudes of passive circuit components, thereby reducing power distribution system and weight. Conventionally, parasitic elements of switching devices and other converter components have operated without contribution to circuit functioning and thus have had a limiting effect on the operating frequency capability of DC-DC converters. In turn, the achievable amount of power system size and weight reduction has been adversely affected. In addition, inefficient converter operation, due to prior switch drive techniques and to types of previously used magnetic components, has adversely affected the development of higher frequency operation of DC-DC converters in the VHF frequency range (VHF: 30-300 MHz).
Communication and radar electronic systems having sensitive data processing requirements further require power line signals with ultra-low (microvolt) noise and ripple. Power supplies, employing traditional pulse width modulation, employ switching of square voltage waveforms which have a high content of high frequency components. Accordingly, such power supplies require added shielding and filtering to obtain low-noise system performance.
Some prior-art efforts have been directed to providing VHF converter operation in power distribution systems. For example, in U.S. Pat. No. 4,980,810, entitled VHF DC-DC POWER SUPPLY OPERATING AT FREQUENCIES GREATER THAN 50 MHz and issued to R. McClanahan et al. on Dec. 25, 1990, a separate oscillator drives a single-ended amplifier circuit. An impedance transformation/isolation circuit couples the single-ended amplifier to an output rectifier circuit. A feedback signal controls preamplifier current to regulate the amplifier and the output voltage.
The McClanahan converter is directed to a radar system application and apparently provides frequency operation up to 50 MHz, and possibly higher. However, the DC-DC converter design employs a separate oscillator and a single-ended amplifier which drive the rest of the circuitry. In single-ended amplifier operation, a single switch cycles ON and OFF to provide a waveform for conversion to a different voltage level.
As such, the overall McClanahan circuit has undesirable inefficiencies, is adversely affected in frequency operation by parasitic circuit parameters, and requires components which are larger and heavier than desirable. Such components directly contribute to the size and weight of a power system in which the converter may be used. It is particularly noteworthy that the prior art single-ended converters are characteristically power level limited at higher frequencies due to inefficiencies encountered with higher frequency operation.
Another prior-art DC-DC converter employs a self-oscillating power train in which a single-ended amplifier is driven by an oscillator to provide high frequency operation but not VHF operation, as disclosed in a group of commonly assigned patents. These patents are perhaps best represented by U.S. Pat. No. 4,605,999, entitled SELF-OSCILLATING HIGH FREQUENCY POWER CONVERTER and issued to W. C. Bowman et al. on Aug. 12, 1986, and U.S. Pat. No. 4,685,041, entitled RESONANT RECTIFIER CIRCUIT and issued to W. C. Bowman et al. et al. on Aug. 4, 1987. As in the McClanahan disclosure, the Bowman single-ended converter is relatively power limited at higher frequencies due to the single-ended amplifier operation. Further, U.S. Pat. No. 4,485,605, entitled HIGH-FREQUENCY DC-DC POWER CONVERTER WITH ZERO VOLTAGE SWITCHING OF SINGLE PRIMARY-SIDE POWER DEVICE and issued to R. L. Steigerwald on Jul. 4, 1989, discloses a DC-DC converter, but, again, it is based on use of a single-ended amplifier.
In another U.S. Pat. No. 4,899,271 entitled POWER SUPPLY CIRCUIT and issued to O. S. Seiersen on Feb. 6, 1990, a power circuit is disclosed, but the disclosure of this patent is particularly directed to certain diode operating features and operates with high harmonic square waves and with adverse parasitic effects.
A need has thus existed for a better DC-DC converter, and particularly a VHF DC-DC converter, in which wider frequency operation can be achieved reliably and effectively with greater facility and with reduced converter size and weight.